The present invention relates to a semiconductor light-emitting device, and in particular, to a semiconductor light-emitting device that employs an AlGaInP-based semiconductor in its light-emitting section.
In order to form a high-intensity semiconductor light-emitting device, it is required to increase the luminous efficiency of its active layer, increase the amount of injection current into the active layer and increase the efficiency of taking out the light emitted from the active layer to the outside of the device.
In order to increase the amount of injection current into the light-emitting section, a current diffusion layer and an intermediate layer or the like capable of improving the amount of injection current without increasing the operating voltage are effective. At the same time, it is required to increase the amount of electrons and holes that contribute to radiative recombination by confining the injected current (electrons and holes) without letting it escape. As a means for confining electrons and holes in the light-emitting layer, a double-hetero (hereinafter referred to as xe2x80x9cDHxe2x80x9d) structure is widely used.
In the DH structure, the active layer is held between semiconductor layers that have a bandgap wider than that of the active layer. Thereby, an energy barrier over which the electrons and holes hardly pass is formed on the upper and lower sides of the active layer, and therefore, the DH structure makes it difficult to let electrons and holes escape. This enables the increase of the probability that the electrons and holes may contribute to the radiative recombination.
The DH structure is widely used also for a semiconductor light-emitting device in which an AlGaInP-based semiconductor is employed in the active layer (refer to Japanese Patent Laid-Open Publication No. HEI 5-335619, page 2, paragraph 0003 and Japanese Patent Laid-Open Publication No. HEI 4-229665, page 2, paragraphs 0003 and 0004).
FIG. 10 shows a prior art semiconductor light-emitting device that has the DH structure.
According to the above-mentioned semiconductor light-emitting device, as shown in FIG. 10, a desired buffer layer 102, an n-AlGaInP clad layer 103, an AlGaInP active layer 104, a p-AlGaInP clad layer 105 and A GaP current diffusion layer 106 are successively laminated on an n-GaAs substrate 101. Further, on the GaP current diffusion layer 106 are successively laminated the other layers of a current blocking layer, a protective layer, an intermediate bandgap layer, a protective layer and so on that are not shown. A p-type electrode 107 is formed on the GaP current diffusion layer 106. An n-type electrode 108 is formed under the n-GaAs substrate 101 by vapor deposition. Subsequently, the n-GaAs substrate 101, the p-type electrode 107, the n-type electrode 108 and so on are formed into the desired shapes so that a semiconductor light-emitting device is completed.
In the above-mentioned semiconductor light-emitting device, a semiconductor having a composition of (AlxG1-x)yIn1-yP (x≈0.7 and y≈0.5) is employed for the n-type clad layer 103 and the p-type clad layer 105. However, in the general semiconductor light-emitting device of the AlGaInP-based semiconductor, a semiconductor having a clad layer composition of (AlxGa1-x)yIn1-yP (0.7xe2x89xa6xxe2x89xa61.0, y≈0.5) is often employed.
FIG. 11 shows a band profile in the vicinity of the active layer of the prior art semiconductor light-emitting device.
As shown in FIG. 11, the upper and lower clad layers have a bandgap wider than that of the active layer, and therefore, an energy barrier is formed on both outer sides of the active layer. This arrangement restrains the phenomenon that the electrons and holes injected into the active layer escape from the active layer to the outside, i.e., overflow. As a result, there increases the probability of radiative recombination of electrons and holes in the active layer, and this allows a high-intensity semiconductor light-emitting device to be obtained.
In the above-mentioned prior art example, the DH structure has been used as a method for confining a large number of electrons and holes injected from the outside of the device in the active layer. However, in a device that has a short wavelength of light emitted from the active layer, the bandgap of the active layer is widened, and the difference in the bandgap between the active layer and the clad layer is reduced.
As described above, if the bandgap difference between the active layer and the clad layer is reduced, then the energy barrier against electrons and holes is reduced. As a result, the effect of confining electrons and holes produced by the clad layer is reduced, and therefore, the electrons and holes easily escape from the active layer. That is, the electrons and holes easily overflow from the active layer. For the above-mentioned reasons, there have been the problems that the luminous efficiency has been reduced in the short-waveform semiconductor light-emitting device and a high-intensity semiconductor light-emitting device has hardly been unable to be obtained.
With regard to electron and hole, it is difficult for hole to overflow since hole has a low mobility, whereas it is easy for electron to overflow since electron has a mobility several tens of times higher than that of hole.
In concrete, with regard to the AlGaInP-based semiconductor light-emitting devices, the overflow does not matter in a device that has an emission wavelength longer than 590 nm, whereas the overflow becomes significant in a device that has an emission wavelength of not greater than 590 nm. This overflow causes a reduction in luminance.
FIG. 12 shows a graph showing the relation between emission wavelength and external quantum efficiency in the semiconductor light-emitting device.
As is apparent from FIG. 12, the overflow of electron becomes particularly significant in the semiconductor light-emitting device that has an emission wavelength equal to or shorter than about 590 nm, and therefore, the luminous efficiency falls with reduced luminance. For the above-mentioned reasons, the luminous efficiency falls in the short-wavelength semiconductor light-emitting device, and it is difficult to obtain a high-intensity semiconductor light-emitting device.
An object of the present invention is therefore to improve the luminance by increasing the probability of radiative recombination of electrons and holes in the active layer of an AlGaInP-based semiconductor light-emitting device of a short wavelength.
In order to solve the aforementioned object, the present invention provides a semiconductor light-emitting device comprising:
a compound semiconductor substrate;
a first-conductive-type clad layer formed on the compound semiconductor substrate;
an active layer formed on the first-conductive-type clad layer and comprised of an AlGaInP-based semiconductor wherein light emitted from the active layer has a wavelength of not greater than 590 nm;
a second-conductive-type clad layer formed on the active layer; and
a semiconductor layer interposed between the active layer and the first-conductive-type clad layer or the second-conductive-type clad layer, wherein
an energy position at a lower end of a conduction band of the semiconductor layer is 0.05 eV to 1.0 eV higher than an energy position at a lower end of a conduction band of the second-conductive-type clad layer in a band profile before formation of a junction between the active layer and the semiconductor layer, and a junction between the semiconductor layer and the first-conductive-type clad layer or the second-conductive-type clad layer.
According to the semiconductor light-emitting device of the above-mentioned construction, since the semiconductor layer is interposed between the active layer and the first-conductive-type clad layer or between the active layer and the second-conductive-type clad layer, the semiconductor layer operates as an energy barrier against electrons to restrain the overflow of electrons from the active layer. As a result, there increases the probability of radiative recombination of electrons and holes in the active layer, and the luminance of the semiconductor light-emitting device can be increased.
In the present specification, the first conductive type means the p-type or the n-type. Moreover, the second conductive type means the n-type when the first conductive type is the p-type, or the second conductive type means the p-type when the first conductive type is the n-type.
The present invention also provides a semiconductor light-emitting device comprising:
a compound semiconductor substrate;
a first-conductive-type clad layer formed on the compound semiconductor substrate;
an active layer formed on the first-conductive-type clad layer and comprised of an AlGaInP-based semiconductor wherein light emitted from the active layer has a wavelength of not greater than 590 nm;
a second-conductive-type clad layer formed on the active layer; and
a semiconductor layer interposed between the active layer and the first-conductive-type clad layer or between the active layer and the second-conductive-type clad layer, wherein
a highest energy position at a lower end of a conduction band of the semiconductor layer is 0.02 eV to 1.0 eV higher than an energy position at a lower end of a conduction band of the second-conductive-type clad layer.
According to the semiconductor light-emitting device of the above-mentioned construction, since the semiconductor layer is interposed between the active layer and the first-conductive-type clad layer or between the active layer and the second-conductive-type clad layer, the semiconductor layer operates as an energy barrier against electrons to restrain the overflow of electrons from the active layer. As a result, there increases the probability of radiative recombination of electrons and holes in the active layer, and the luminance of the semiconductor light-emitting device can be increased.
The present invention also provides a semiconductor light-emitting device comprising:
a compound semiconductor substrate;
a first-conductive-type clad layer formed on the compound semiconductor substrate;
an active layer formed on the first-conductive-type clad layer and comprised of an AlGaInP-based semiconductor wherein light emitted from the active layer has a wavelength of not greater than 590 nm;
a first second-conductive-type clad layer formed on the active layer;
a second second-conductive-type clad layer formed on the first second-conductive-type clad layer; and
at least one semiconductor layer interposed between the first second-conductive-type clad layer and the second second-conductive-type clad layer, wherein
an energy position at a lower end of a conduction band of the semiconductor layer is 0.05 eV to 1.0 eV higher than an energy position at a lower end of a conduction band of the second second-conductive-type clad layer in a band profile before formation of a junction between the first second-conductive-type clad layer and the semiconductor layer and a junction between the semiconductor layer and second second-conductive-type clad layer.
According to the semiconductor light-emitting device of the above-mentioned construction, since the semiconductor layer is interposed between the first second-conductive-type clad layer and the second second-conductive-type clad layer, the semiconductor layer operates as an energy barrier against electrons to restrain the overflow of electrons from the active layer. As a result, there increases the probability of radiative recombination of electrons and holes in the active layer, and the luminance of the semiconductor light-emitting device can be increased.
The present invention also provides a semiconductor light-emitting device comprising:
a compound semiconductor substrate;
a first-conductive-type clad layer formed on the a compound semiconductor substrate;
an active layer formed on the first-conductive-type clad layer and comprised of an AlGaInP-based semiconductor wherein light emitted from the active layer has a wavelength of not greater than 590 nm;
a first second-conductive-type clad layer formed on the active layer;
a second second-conductive-type clad layer formed on the first second-conductive-type clad layer; and
at least one semiconductor layer interposed between the first second-conductive-type clad layer and the second second-conductive-type clad layer, wherein
an energy position at a lower end of a conduction band of the semiconductor layer is 0.02 eV to 1.0 eV higher than an energy position at a lower end of a conduction band of the second second-conductive-type clad layer.
According to the semiconductor light-emitting device of the above-mentioned construction, since the semiconductor layer is interposed between the first second-conductive-type clad layer and the second second-conductive-type clad layer, the semiconductor layer operates as an energy barrier against electrons to restrain the overflow of electrons from the active layer. As a result, there increases the probability of radiative recombination of electrons and holes in the active layer, and the luminance of the semiconductor light-emitting device can be increased.
The present invention also provides a semiconductor light-emitting device comprising:
a compound semiconductor substrate;
a first first-conductive-type clad layer formed on the compound semiconductor substrate;
a second first-conductive-type clad layer formed on the first first-conductive-type clad layer;
at least one semiconductor layer interposed between the first first-conductive-type clad layer and the second first-conductive-type clad layer;
an active layer formed on the second first-conductive-type clad layer and comprised of an AlGaInP-based semiconductor wherein light emitted from the active layer has a wavelength of not greater than 590 nm; and
a second-conductive-type clad layer formed on the semiconductor layer, wherein
an energy position at a lower end of a conduction band of the semiconductor layer is 0.05 eV to 1.0 eV higher than an energy position at a lower end of a conduction band of the first first-conductive-type clad layer in a band profile before formation of a junction between the first first-conductive-type clad layer and the semiconductor layer and a junction between the semiconductor layer and second first-conductive-type clad layer.
According to the semiconductor light-emitting device of the above-mentioned construction, since the semiconductor layer is interposed between the first first-conductive-type clad layer and the second first-conductive-type clad layer, the semiconductor layer operates as an energy barrier against electrons to restrain the overflow of electrons from the active layer. As a result, there increases the probability of radiative recombination of electrons and holes in the active layer, and the luminance of the semiconductor light-emitting device can be increased.
The present invention also provides a semiconductor light-emitting device comprising:
a compound semiconductor substrate;
a first first-conductive-type clad layer formed on the compound semiconductor substrate;
a second first-conductive-type clad layer formed on the first first-conductive-type clad layer;
at least one semiconductor layer interposed between the first first-conductive-type clad layer and the second first-conductive-type clad layer;
an active layer formed on the second first-conductive-type clad layer and comprised of an AlGaInP-based semiconductor wherein light emitted from the active layer has a wavelength of not greater than 590 nm; and
a second-conductive-type clad layer formed on the semiconductor layer, wherein
an energy position at a lower end of a conduction band of the semiconductor layer is 0.02 eV to 1.0 eV higher than an energy position at a lower end of a conduction band of the first first-conductive-type clad layer.
According to the semiconductor light-emitting device of the above-mentioned construction, since the semiconductor layer is interposed between the first first-conductive-type clad layer and the second first-conductive-type clad layer, the semiconductor layer operates as an energy barrier against electrons to restrain the overflow of electrons from the active layer. As a result, there increases the probability of radiative recombination of electrons and holes in the active layer, and the luminance of the semiconductor light-emitting device can be increased.
In the semiconductor light-emitting device of one embodiment, the semiconductor layer is either one of a group consisting of a GaP layer, an AlxGa1-xP (0 less than xxe2x89xa60.7) layer and an (AlxGa1-x)yIn1-yP (0 less than xxe2x89xa60.7, 0.65xe2x89xa6y less than 1) layer.
In the semiconductor light-emitting device of the above-mentioned embodiment, the semiconductor layer is either one of the GaP layer, the AlxGa1-xP (0 less than xxe2x89xa60.7) layer and the (AlxGa1-x)yIn1-yP (0 less than xxe2x89xa60.7, 0.65xe2x89xa6y less than 1) layer. Therefore, the overflow of electrons from the active layer can reliably be restrained.
In the semiconductor light-emitting device of one embodiment, the semiconductor layer has a thickness range of 10 xc3x85 to 500 xc3x85.
In the semiconductor light-emitting device of the above-mentioned embodiment, the thickness of the semiconductor layer is within the range of 10 xc3x85 to 500 xc3x85. Therefore, the overflow of electrons from the active layer can reliably be restrained, and crystal defect due to lattice mismatch can be restrained. That is, when the thickness of the semiconductor layer is smaller than 10 xc3x85, the overflow of electrons cannot reliably be restrained. When the thickness of the semiconductor layer exceeds 500 xc3x85, the crystal defect due to lattice mismatch occurs.
In the semiconductor light-emitting device of one embodiment, the semiconductor layer has a thickness range of 10 xc3x85 to 140 xc3x85.
Since the layer having lattice mismatch is inserted, wafer warp occurs. The wafer warp significantly occurs when a wafer is thinned by grinding before the wafer obtained after growth is divided into device elements. However, in the semiconductor light-emitting device of the above-mentioned embodiment, the layer thickness is set smaller than 500 xc3x85 or, in particular, not greater than 140 xc3x85. Therefore, the wafer warp can reliably be restrained. Accordingly, it is preferable to set the thickness of the semiconductor layer within the range of 10 xc3x85 to 140 xc3x85.
In the semiconductor light-emitting device of one embodiment, the active layer is an SQW active layer or an MQW active layer.
In the semiconductor light-emitting device of one embodiment, the SQW layer or the MQW layer is comprised of a plurality of barrier layers and at least one well layer, and
the energy position at the lower end of the conduction band from a vacuum level in part or all of the barrier layers is 0.05 eV to 1.0 eV higher than the energy position at the lower end of the conduction band from the vacuum level in (AlxGa1-x)yIn1-yP (x=0.7, y=0.51).
According to the semiconductor light-emitting device of the above-mentioned embodiment, the energy position at the lower end of the conduction band from the vacuum level in part or all of the barrier layers is 0.05 eV to 1.0 eV higher than the energy position at the lower end of the conduction band from the vacuum level in (AlxGa1-x)yIn1-yP (x=0.7, y=0.51). Therefore, electrons can reliably be confined in the well layer. As a result, there increases the probability of radiative recombination of electrons and holes in the active layer, and the luminance of the semiconductor light-emitting device can be increased.
The present invention also provides a semiconductor light-emitting device comprising:
a compound semiconductor substrate;
a first-conductive-type clad layer formed on the compound semiconductor substrate;
an active layer formed on the first-conductive-type clad layer; and
a second-conductive-type clad layer formed on the active layerm, wherein
the active layer is an SQW active layer or an MQW active layer comprised of an AlGaInP-based semiconductor,
the SQW layer or the MQW layer is comprised of a plurality of barrier layers and at least one well layer, and
an energy position at a lower end of a conduction band from a vacuum level in part or all of the barrier layers is 0.05 eV to 1.0 eV higher than an energy position at a lower end of a conduction band from a vacuum level in (AlxGa1-x)yIn1-yP (x=0.7, y=0.51).
According to the semiconductor light-emitting device of the above-mentioned construction, the energy position at the lower end of the conduction band from the vacuum level in part or all of the barrier layers is 0.05 eV to 1.0 eV higher than the energy position at the lower end of the conduction band from the vacuum level in (AlxGa1-x)yIn1-yP (x=0.7, y=0.51). Therefore, the overflow of electrons from the active layer can be restrained by reliably confining the electrons in the well layer. As a result, there increases the probability of radiative recombination of electrons and holes in the active layer, and the luminance of the semiconductor light-emitting device can be increased.
In the semiconductor light-emitting device of one embodiment, the barrier layers are either one of a group consisting of a GaP layer, an AlxGa1-xP (0 less than xxe2x89xa60.7) layer and an (AlxGa1-x)yIn1-yP (0 less than xxe2x89xa60.7, 0.65xe2x89xa6y less than 1) layer.
According to the semiconductor light-emitting device of the above-mentioned embodiment, the barrier layers should preferably be either one of the GaP layer, the AlxGa1-xP (0 less than xxe2x89xa60.7) layer and the (AlxGa1-x)yIn1-yP (0 less than xxe2x89xa60.7, 0.65xe2x89xa6y less than 1) layer in terms of reliably restraining the overflow of electrons from the active layer.
In the semiconductor light-emitting device of one embodiment, the semiconductor layer or each of the barrier layers is the second conductive type.
In the semiconductor light-emitting device of one embodiment, the semiconductor layer or each of the barrier layers has a carrier density of 1xc3x971017 to 5xc3x971018 cmxe2x88x923.
In the semiconductor light-emitting device of one embodiment, the first conductive type is n-type, and the second conductive type is p-type.